Operating
/Action
2.2.1.1 Reset Circuit
The 68000 CPU contains the reset terminal, which is bidirectional and can initialize the system
either from inside or outside the CPU.
entire system (the CPU and the external devices) can be
initialized if both the HALT (CPU pin 20) and RESET (CPU pin 21) signals are active
simultaneously. By executing a RESET instruction, a RESET pulse from inside the CPU can also be
issued to reset all the devices
to the RESET line.
circuit uses an
to
monitor the supply voltage and reset the CPU if a voltage level less than 4.25 V is detected. The
reset time is approximately 840 ms.
7
+
RESET
M51953BFP
(lCl)
c
Figure 2-33. Reset Circuit
2.2.1.2 Bus Control Circuit
The 68(111 CPU outputs the R/W (read/write), AS (address
strobe);
(processor status) signals to
uses these signals to generate the RD
(read strobe),
(wait control),
(interrupt control), and
(bus error) signals.
CPU
68000
R/W
●
,2
●
Address Data ‘
D w R
Bus
Bus
Figure 2-34. Bus Control Circuit
2-22
Rev.
